compiler: a labeled for/while expression returns an unspecified value when break has no value

[perillo]

Zig Version

0.11.0-dev.6417+0bb178bbb

Steps to Reproduce and Observed Behavior

const std = @import("std");
const debug = std.debug;

pub fn main() void {
    var a: *isize = blk: for (0..10) |_| {
        break :blk;
    };
    debug.print("a: {}\n", .{a});

    var b: *isize = blk: while (true) {
        break :blk;
    };
    debug.print("b: {}\n", .{b});
}

$ zig run main.zig

a: isize@0
b: isize@7ffc30760750

NOTE: the output depends on the order of statements.
I got a consistent output when moving the b variable definition before a:

b: isize@0
a: isize@20

Expected Behavior

The compiler should report an error instead of causing an undefined behavior.

NOTE: I used a pointer variable to check if the value was the same as when using undefined.